Pressure-sensitive magnetic transfer elements



United States Patent O 3,496,015 PRESSURE-SENSITIVE MAGNETIC TRANSFERELEMENTS Douglas A. Newman, Glen Cove, and Allan T. Schlotzhauer, LocustValley, N.Y., assignors to Columbia Ribbon and Carbon Manufacturing Co.,Inc., Glen Cove, N.Y., a corporation of New York No Drawing. Filed Nov.9, 1966, Ser. No. 594,338 Int. Cl. B41c 1/06; B44d 1/02, 1/18 US. Cl.117-235 6 Claims ABSTRACT OF THE DISCLOSURE Pressure-sensitive transferelements for the placement of magnetically-sensible images under variousconditions of use. The imaging layer has a porous resinous bindercontaining pressure-exudable liquid ink. The ink comprises a liquid oilvehicle and magnetic pigment having an oil absorption value below 20 anda tap density value above 20.

Magnetic transfer sheets and ribbons are well known to the art. Most ofsuch elements comprise a plastic film foundation carrying a frangiblepressure-transferable layer based upon a binder material such as wax orsynthetic resin and containing a magnetizable pigment such as black ironoxide.

Magnetic sensing systems and equipment have definite critical toleranceswhich, if exceeded, result in a failure of the system and a rejection ofthe data being processed. For MICR work the American Bankers Associationhas established tolerances with respect to magnetic amplitude signallevel, voids and edge tolerances, among others. The signal level of aspecific magnetic character must equal from 50% to 200% of a standardlevel known as the May 27, 1958 Reference measured on a General ElectricMagnetic Printing Tester; the voids in the character must be no longerthan can be completely confined in a 0.006 by 0.006 square, and the edgeirregularities must not extend more than -0.0025" from the nominal edgedimension of the character.

While frangible magnetic transfer elements are generally suitable fordirect image work Where the imaging pressure is applied directly to thetransfer element as a sharp blow delivered by an impact device such as atypewriter bar, they are not suitable for use in the interior ofmulti-sheet forms or with pressure-roller imaging devices. Frangibletransfer layers have a narrow latitude with respect to transferpressures. Below a particular level of pressure no transfer occurs; at aparticular narrow level a perfect transfer is possible; and above thatlevel excess transfer occurs. The defects resulting from too little ortoo much pressure are primarily voids, edge irregularities and excessbackground staining or formation of extraneous particles around theimages. When such frangible magnetic transfer elements are used in theinterior of multi-sheet forms or are impressed by a roller-pressuredevice, the level of pressure transmitted to the transfer layer is onthe low side so that little or no transfer may occur and the imagesformed, if any, may contain large voids and edge irregularities whichrender them incapable of being accurately magnetically sensed or read.Attempts to increase the magnetic amplitude or signal level of such weakimages by increasing the amount of magnetic pigment in the frangibletransfer composition results in a transfer element which isunsatisfactory for direct impact pressure use due to the high signallevel of the background staining produced in this manner and the highsignal level of the edge irregularities formed. Thus it is 3,496,015Patented Feb. 17, 1970 not possible to produce a frangible magnetictransfer element capable of reliable use in the variety of applicationsencountered for normal business use.

It has been recognized that pressure-sensitive squeezeout type transfercompositions containing ink comprising liquid oil and dispersed pigmentproduce a uniform exudation of ink under the elfects of various typesand degrees of imaging pressure to form smudge-resistant images. Whileimages produced from such compositions are relatively free of voids andedge irregularities, such compositions function in a squeeze-out mannerand thus do not transfer a heavy solid mass of composition, as in thecase with frangible transfer compositions. While in some cases it ispossible to exceed the minimum 50% signal level with conventionalsqueeze-out transfer sheets, the signal level will drop below the 50%value very often depending upon the conditions of use of the transfersheets such as the amount of pressure applied, the quality of the copypaper and the position of the transfer sheet relative to the imagingdevice. For practical purposes it is required that the transfer sheet iscapable of producing images having a signal level equal to at least andnot exceeding of standard so that the absolute signal level toleranceswill be attained under the varying conditions of use.

However it has been discovered that the tolerances established formagnetic sensing cannot be reliably satisfied, particularly inmulti-sheet form imaging and roller pressure-imaging, through the use oftransfer elements containing frangible or pressure-transferrablemagnetic layers. To the contrary, the magnetic layer must be one whichdoes not transfer as a mass under the elfects of imaging pressure butrather which functions by squeezing out or exuding an amount of liquidmagnetic ink containing a large amount of magnetic pigment under theeffects of even slight imaging pressure of any type. The presentinvention is concerned with providing improved compositions and transfersheets of this type.

Pressure-sensitive transfer sheets of the squeeze-out type are known inthe carbon paper and ribbon field, such as US. Patents Nos. 2,820,717and 3,037,879. Attempts to produce magnetic transfer sheets bysubstituting conventional magnetic pigments for the carbon black andother pigments of such known carbon papers containing liquid oilvehicles have not produced completely satisfactory results sinceproblems accompany the inclusion of conventional magnetic pigments inliquid oily vehicles in such formulations in sufficiently high amountsto produce duplicate images of sufficient magnetic amplitude to bereliably accurately sensed with scanning equipment currently used,particularly when positioned in the interior of a multi-sheet form.Beyond a certain maximum amount the conventional magnetic pigmentsrender the oily vehicle so thick that it cannot be exuded underpressure, and at or below such maximum amount the images producedcontain an insuflicient amount of the magnetic pigment to insure thegeneration of the required magnetic amplitude or signal levelparticularly in cases where such transfer sheets are used in theinterior of multisheet forms or are impressed by means of rollerpressure.

With these problems in mind, it is the object of this invention toprovide pressure-sensitive transfer elements such as sheets and ribbonswhich contain large amounts of magnetizable pigment and which are sosensitive to imaging pressure as to produce uniform, sharp dupicateimages of high magnetic amplitude even when positioned in the interiorof multi-sheet forms and when subjected to roller pressure.

This and other objects and advantages of the inven- 3 tion will be clearto those skilled in the art in the light of the following disclosure.

We have discovered that improved pressure-sensitive transfer elements ofthe non-frangible squeeze-out type can be formulated so as to produceduplicate magnetic images having the required signal level byformulating the pressure-exudable magnetic ink from a high amount ofmagnetizable pigment of a particular specific type in association with aliquid oily vehicle which the magnetizable pigment absorbs to acomparatively low extent.

The magnetizable pigments suitable for use according to the presentinvention are those which have an aver-age particle size of less than 5microns and preferably less than 1 micron and have a minimum ASTM tapdensity value above about grams per cubic inch, and have a maximum ASTMoil absorption value below about 20 measured by the spatula method. Thetap density of the magnetic pigment is determined by the ASTM method byweighing the maximum amount of the particular magnetic pigment which canbe compacted into the space of a cubic inch under the effects of tappingpressure applied against the container. This is a measure of the surfaceproperties and mobility of the pigment since the smoother and moreregular the surface the more easily the particles can move about and themore particles which can be compressed into a "given area.

The oil absorption value is a measure of the minimum weight of pure rawlinseed oil required to completely wet 100 grams of the particularmagnetizable pigment to form a stiff putty-like paste that does notbreak. Pigments which absorb the oil to a high degree require much moreoil to wet 100 grams of the pigment than pigments which absorb the oilto a low degree.

While in the carbon paper field it has been a desirable feature to usehigh oil-absorbing pigments in squeezeout type carbons in order toproduce dark-writing sheets, this consideration does not pertain to theproduction of magnetically-sensible images since the magnetic amplitudewhich the images are capable of generating is the essential property. Animage which contains black pigment having oil absorbed therein will bemuch blacker to the eye but will contain less pigment than an imagewhich contains black pigment having a smaller amount of oil absorbedtherein and formed from the same type of squeeze-out sheet incorporatingthe same proportion of oil and pigment. For magnetic sensing it isnecessary that the maximum possible amount of magntizable pigment betransferred to the copy sheet in order to generate the greatest possibleamplitude, and the intensity or visual readability of such images is ofsecondary importance.

Conventional magnetic ink character recognition systems (MICR) aresufficiently sensitive to detect and read images which generate amagnetic wave form having an amplitude equal to or above 50% ofstandard. While it is possible to use magnetic inks having an amplitudeof 50% of standard for direct printing Work since the sharpness of theprinted characters and the weight of the printed ink is easy to controland to maintain constant, it is not possible to obtain reliablysatisfactory results using such inks in the present transfer sheets inview of the important differences in their end use which make itimpossible to control the sharpness of the formed image and its contentof magnetic to the same extent as is possible in a printing operation.When the transfer sheet is used in the interior of -a multi-sheet formor is impressed by roller pressure, it will liberate less magnetic inkand generate a lower amplitude than when it is used for directimpression Work or is impressed by a type bar. Even when used inidentical manner, the magnetic amplitude of the formed images will varydepending on the location of the transfer sheet within the form or theefficiency or degree of wear of the pressure roller impression device.

In actual practice we have found that the present inks must be capableof generating a magnetic amplitude of at least of standard when usedunder ideal conditions and preferably not in excess of 150% of standard.We have found that if the magnetic ink has this minimum capacity whenthe images are formed by typing directly against the transfer sheet andtransferring the ink to a copy sheet which is well receptive thereto,then the present transfer sheets will be operative under all normaloperating conditions such as in the interior of multisheet forms andunder the effects of roller pressure. While the amplitude of the imagesformed by these less efficient methods will be far less than 90% ofstandard, it will never fall below the 50% value tolerance ofconventional MIRC systems.

We have discovered that the magnetizable pigments heretofore used in thetransfer sheet field do not provide reliably satisfactory results underall operating condi tions when used as the pigment in liquid oilvehicles in squeeze-out type transfer sheets particularly Whenpositioned in the interior of multi-sheet forms or imaged by means of apressure roller. The most commonly used magnetic pigment is IRN-lOOwhich is a ferroso-ferric oxide (Fe O commercially available from C. K.Williams & Co., Easton, Pa. While this material is quite suitable foruse in frangible transfer layers, it is not reliably suited to themulti-use transfer elements of the present invention which contain aliquid oil vehicle because of its rough surface characteristics and itshigh oil absorption. The tap density of this material, having an averageparticle size of less than 1 micron, is about 12:1 gms./ cu. in. and theoil absorption value is about 50. This is in contrast with the magneticpigments for use herein which have oil absorption values below about 20and tap density values above about 20. One such preferred pigment isM07029, a ferroso-ferric oxide commercially available from Pfizer & Co.,New York, which has a tap density of about 33 and an oil absorptionvalue of about 12.

The following is a list of other magnetizable iron oxide pigmentscommercially available from Pfizer & Co. which are suitable for useaccording to this invention. These suitable materials represent only afraction of the magnetizable pigments commercially available for avariety of uses, such as in printing inks and magnetic tapes, most ofwhich are unsuitable for use according to the present invention.

Tap Density, Oil Absorption, Trade Designation gms./cu. in. gms./ gms.

MO-8629- 30 14 MO8029 30 14 MO-7029- 33 12 The following example isgiven by way of illustration and should not be considered limitative.

The magnetic pigment is first dispersed in at least an equal weight ofone or more of the oils and is thereafter added to the solution of theresin containing the remainder of the oil. The composition is thencoated onto a flexible foundation such as paper or plastic film anddried by evaporation of the volatile solvents to form the solidpressure-sensitive squeeze-out layer.

An attempt to substitute an equal amount of a more conventional magneticpigment such as IRN-100 for the MO-7029 in the above formulation resultsin a layer which exudes less magnetic pigment under the effect ofimaging pressure to produce images having an inferior signal strength.The oil is absorbed by the IRN-lOO so that the ink phase has little orno fiowability under pressure. The addition of several more parts byweight of oil renders the ink phase fluid and permits the formation oflegible black duplicate images under the effects of direct typingpressure. However, the magnetic amplitude of such images is only about50% of standard compared to a magnetic amplitude of about 120% ofstandard obtained with images formed from the transfer sheet of theexample.

Aside from the critical limitations with respect to the magnetizablepigment and the liquid nature of the oil vehicle, the other componentsof the present squeeze-out transfer sheets and their proportions are thesame as those used heretofore in the carbon paper field, as illustratedfor instance by U.S. Patents Nos. 2,820,717 and 3,037,879. While vinylresin binders are preferred, other materials such as the acrylic resinsand polycarbonates, well known in the squeeze-out carbon paper art, maybe used. The'oily vehicle must be one which is rapidly flowable atordinary room temperature and which is substantially unabsorbed by themagnetizable pigment.

The present squeeze-out layers preferably comprise 1 part by weight ofresinous binder material, from 1 to 4 parts by weight of liquid oilvehicle and from 2 to 5 parts by weight of the magnetic pigment. Thecoating solvent may be any suitable volatile organic liquid, andevaporation of the solvent is preferably caused by the application ofheat.

In cases where the foundation sheet is paper which tends to absorb theoil from the ink layer, it is preferred to position an oil-imperviousresinous intermediate layer between the ink layer and the foundation.However, it is preferred to use a plastic film foundation such aspolyethylene terephthalate polyester (Mylar) or similar film and to usea plastic intermediate layer between the film and the ink layer to forma bond between the tWo and to prevent pressure-transfer of the latter inmass, particularly at the higher pressures exerted by some magneticprinting devices.

Variations and modifications may be made and po tions of theimprovements may be used without others.

We claim:

1. A pressure-sensitive squeeze-out type magnet transfer elementcomprising a flexible foundation havir thereon a layer capable ofexuding a liquid magnetic it under the effects of varying degrees ofimaging pressu. to produce images having a magnetic signal level of froabout to of standard, said layer having a no: transferable porous,spongy structure comprising 1 pa by weight of resinous binder materialcontaining with the pores thereof a pressure-exudable mganetic ink corprising from about 1 to 4 parts by weight of a liqu oil which issubstantially incompatible with said bind material and from about 2 to 5parts by weight of a ma netic pigment which has an oil absorption valuebelo about 20 and a tap density value above about 20.

2. A transfer element according to claim 1 in Whit the foundation isplastic film.

3. A-transfer element according to claim 1 in Whit the liquid oilcomprises at least one material selectt from the group consisting ofbutyl stearate, sulfonatc vegetable oil and refined rapeseed oil.

4. A transfer element according to claim 1 in Whit the magnetic pigmentcomprises iron oxide.

5. A transfer element according to claim 1 in which tl binder materialcomprises a vinyl resin.

6. A transfer element according to claim 2 in Whit the vinyl resincomprises a copolymer of vinyl ChlOl'i( and vinyl acetate.

References Cited UNITED STATES PATENTS 3,061,454 10/1962 Graf et al.11736 3,072,577 1/1963 Miller et a1. 25262.54 3,194,676 7/1965 Krumbeinet al. 25262.54 3,247,117 4/1966 Shoemaker et a1. 25262.54

OTHER REFERENCES The Chemical Trade Journal and Chemical Enginee Jan.14, 1927, vol. 80, p. 35. Drugs, Oils and Paints, vc 46, No. 9, p. 330.Reichard-Coulston, Inc.

us. c1. X.R.

